Scientists at the University of Copenhagen have identified a hidden defense mechanism in aging muscle that sacrifices strength to shield cells from damage. The work, published in Nature Aging, shows that a decline in the mitochondrial lipid cardiolipin drives a shift from fast‑twitch to slow‑twitch fibers, and that partially restoring cardiolipin reverses muscle wasting and prevents premature death in mice.
Cardiolipin loss disrupts mitochondrial structure and function
Cardiolipin is a specialized fat molecule that resides almost exclusively in the inner membrane of mitochondria, where it maintains the membrane’s folded architecture essential for energy production. Analysis of muscle samples from both mice and humans revealed that cardiolipin levels fall with age or disease, accompanied by structural abnormalities and reduced mitochondrial performance.
To test whether the loss of cardiolipin directly causes age‑related changes, researchers experimentally lowered cardiolipin in young mice. The treated animals displayed a muscle‑fiber composition that mirrored natural aging: a reduction in fast‑twitch fibers, which generate rapid, powerful movements, and an increase in slow‑twitch fibers, which support endurance but rely heavily on mitochondria. The similarity suggests that cardiolipin depletion is a driver, not merely a by‑product, of the fiber‑type shift.
Protective trade‑off mediated by ROS and ERRγ
When cardiolipin drops, damaged mitochondria release large amounts of reactive oxygen species (ROS). While ROS can damage cellular components, they also serve as signals that initiate protective responses. The team found that ROS signaling triggers the conversion to slow‑twitch fibers. Treating cardiolipin‑deficient muscle cells with an antioxidant reduced ROS and blunted the fiber‑type transition, indicating that ROS are essential for the switch.
A protein called estrogen‑related receptor gamma (ERRγ) orchestrates this response. ERRγ directs mitochondrial re‑organization and the change in fiber characteristics. In laboratory muscle cells, inhibiting ERRγ stopped the transition entirely, confirming its central role.
Further experiments showed that mice with low cardiolipin absorbed more glucose from the bloodstream, but instead of using the sugar for energy, the muscle cells diverted it to synthesize antioxidants. This metabolic rerouting helps neutralize excess ROS, reinforcing the protective nature of the fiber conversion.
“The fiber switch is not the muscle failing, but the muscle trading power for protection,” explains Assistant Professor Fabian Finger, first and co‑corresponding author. “When we gave the mice antioxidants to mop up the ROS, their muscles fared worse, not better.”
Therapeutic implications and future directions
Restoring cardiolipin to roughly two‑thirds of normal levels in the mouse model reversed signs of muscle wasting and completely averted premature death, highlighting the molecule’s therapeutic potential. Although the protective mechanism was demonstrated in mice, human muscle samples confirmed that cardiolipin also declines with age, suggesting relevance to people.
The FDA recently granted accelerated approval to elamipretide, a drug that stabilizes cardiolipin, for the rare Barth syndrome. This approval indicates that pharmacologically targeting cardiolipin is feasible, though its efficacy for ordinary age‑related muscle loss remains to be tested.
ERRγ presents another druggable target. Belonging to the nuclear‑receptor family, ERRγ is already the focus of small‑molecule drugs that account for about 10‑15 % of FDA‑approved medicines. Pre‑clinical studies are exploring ERRγ activators for other conditions, and the current findings suggest that modulating ERRγ could promote healthy muscle adaptations under mitochondrial stress.
Senior author Zachary Gerhart‑Hines, Associate Professor at the NNF Center for Basic Metabolic Research, notes, “What encourages me most is that even a partial recovery of cardiolipin was enough to bring the muscle back. The question now is whether we can increase cardiolipin in aging muscle or target ERRγ to promote healthy adaptations. This is where the therapeutic potential lies.”
The research involved more than 20 institutions and received funding from the Novo Nordisk Foundation, European Research Council, Lundbeck Foundation, U.S. National Institutes of Health, and others. While human trials are needed, the study opens a promising avenue for combating sarcopenia and other age‑related muscle disorders.
Steve Lopez is a Senior Editorial Columnist and Health & Public Policy reporter for News Raise. Steve focuses on healthcare advancements, medical technologies, and public health policies.
